STIHL trimmer burps fuel out tank vent hose

[Merkava_4]

STIHL FS 91 R

If I start up the trimmer and bring to full throttle to warm it up and then shut it down, about 30 seconds after shut down, fuel will burp out of the brass vent port in the air filter housing and then run along the bottom of the black plastic recess where the air filter seal makes contact. That's the little brass hole you see at the top left of the air filter housing in the eBay picture I copied. Is this normal behavior?

 

[DND 9000]

Sounds like your tank vent is faulty. That tank vent should not hold vacuum, but it shoud hold 0,5 bar pressure for at least 20 sec. If it drops faster the leak has to be found.

 

[Merkava_4]

Those vents are complicated. A human cannot activate the vent. It has to be done with the STIHL test instrument.

It seems as though the fuel drizzle out the air cleaner is the worst after a cold start. Subsequent warm starts I get mainly bubbles out the port.

The last time I had to change the tank vent was because the tank was getting pressurized and the fuel/air mixture was changing with fuel volume.

As of now it seems like the fuel/air mixture is remaining constant which is a good thing.

 

[EFSM]

Those vents are complicated. A human cannot activate the vent. It has to be done with the STIHL test instrument.

It seems as though the fuel drizzle out the air cleaner is the worst after a cold start. Subsequent warm starts I get mainly bubbles out the port.

The last time I had to change the tank vent was because the tank was getting pressurized and the fuel/air mixture was changing with fuel volume.

As of now it seems like the fuel/air mixture is remaining constant which is a good thing.

That vent simply lets air in but not out. It should hold vacuum applied to the fitting but not pressure. Do you have a pressure/vacuum tester?

 

[Merkava_4]

That vent simply lets air in but not out. It should hold vacuum applied to the fitting but not pressure. Do you have a pressure/vacuum tester?

I'm saving my pennies up for a STIHL 0000-850-1300